Control apparatus



Jan. 3l, E950.

D. l.. MARKUSEN CONTROL APPARATUS Filed April e, i946 .2 Sheets-Sheet l lha SN IIIIPTI ABY D. L.. MARKUSEN Jan., 3l, i950 CONTROL APPARATUS Filed April 641 1946 2 Sheets-Sheet 2 HTTO/f/VEY Patented Jan. 3l, 1950 CONTROL APPARATUS David L. Markusen, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application April 6, 1946, Serial N0. 660,099

20 Claims.

The present invention relates to improved control apparatus for a plural zone temperature control system wherein the supply of temperature changing medium, its temperature. or both, are individually controlled for the respective zones and wherein the total supply of medium7 its temperature, or both, are controlled in response to the cumulative demand of all of the zones.

It is known that a condition such as temperature is more eifectively controlled if the supply of condition changing medium, or its temperature, or both, are reasonably close to that required to maintain the desired condition in the space being treated. Obviously. this problem becomes more complicated as additional spaces must be treated or conditioned from a single supply 0f condition changing medium, for the supply must then be adequate for the cumulative demand of all of the spaces. It is thus an object of the present invention to provide a condition controlling system for a plurality of spaces or zones wherein each of the zones is individually controlled and wherein the condition changing medium supplied to the zones is just adequate to meet the total demand of all of the zones.

It is an additional object to provide an electronic control system for individually controllingA a plurality of zones and for controlling the zones as a whole. Closely related to this object isthe desire to provide apparatus of the sort described useful in buildings and ideally suited to railway cars, aircraft and the like.` Additionally, it is desired to provide a system easily compensated and readily adapted to stage and proportioning control of the condition changing apparatus.

It is an additional object to provide such an electronic system using a single amplifier to respond to conditions in a plurality of locations and to control a plurality of condition changing devices.

It is a further object to provide control apparatus of the sort described for a pressurized aircraft cabin wherein the air supplied to the cabin is heated to some extent by the compressing of the same, wherein the air supplied to each zone L may be further heated to meet the demands of the individual zones, and wherein the heat of compression of the air supplied may be reduced to lower the temperature of an overheated Zone.

It is also an object to provide a control systemA comprising a plurality of series connected `networks wherein each network may be individually used for controlling function and wherein the entire series may be usedI for an additional con?` trolling function.

It is an additional object to provide temperature control apparatus for a plurality of Zones: wherein the supply of temperature changing medium to each zone is varied in response to the,y demand in said zone and wherein the tempera'' ture changing ability of the medium supplied to the zones as a whole is controlled to meet the cumulative demands of all the Zones.

It is a further object to provide means for.' controlling the cooling of Ventilating air being supplied to a plurality of zones in response to the. cumulative demand for said cooling. Y 2

It is also an object to provide means for controlling the change of temperature of a mediumv eing supplied to a plurality of zones in response to the total requirements for change of one sort minus the total requirements for change of an-l other sort. I

It is a further object to provide a plurality of connected electrical networks capable of beingn unbalanced in response to a condition and to be partially rebalanced, at least one of said networks being capable of being unbalanced due to cumulative unbalances of other networks only partially` rebalanced.

These and other objects will become apparent upon a study of the present specification and drawings wherein:

Figure 1 is a schematic illustration of the pres. ent invention applied to an aircraft having four r conditioned Zones; and

Figure 2 is a schematic illustration of the in vention applied to a structure heated by hot water and having four zones. i

Figure l, as above noted, shows schematically the present invention as applied to a large pressurized cabin passenger carrying airplane. vInthis airplane, not shown, the cabin is divided into iour zones, |0|, 20|, 38| `and 40|. As is wellv known in aircraft of this type, the air for ventilation is first compressed and then delivered to the cabin, which is sealed, and the air is released from the cabin through a regulating valve ad-A justed to maintain a desired pressure within the cabin space. The air may be compressed by the.' turbosuperchargers of the engines of the aircraft or by auxiliary compressing means, notshown, and the compressed air is then delivered through ducts lil and Il and after-coolers I2 and I3, respectively to a main duct i4 from which the air is distributed to the zones of the cabin.. Compressed air from duct I4 is delivered to zone- |B| through duct |62 and heat exchanger |03, to zone 20| through duct 202 and heat exchanger- 203, to zone BDI through duct 302,' and heat ex` changer 303, and through duct 402 and heat exchanger 403 to Zone 40 It is well known that the compressing of air results in the generation of heat, consequently the air delivered through branches I and to duct I4 is heated to an extent depending upon the amount of the compressing of the same. Under some conditions, the amount of heat added to the air by compressing will be just sufficient to meet the heat demands of the respective zones. However, under some conditions, the heat of compression will be excessive and the air delivered to the zones will therefore be too warm. To permit cooling of the air delivered from the compressors, after-coolers I2 and i3 are provided. These aftercoolers are merely heat exchangers through which the compressed air passes through one set ci passages and through which cooling air passes through other passages. The cooling air for the heat exchangers enters through ram air inlets I6 and I1 and discharges through conduits I8 and I9, respectively. The flow of cooling air through cooler I2 and conduit I8 is controlled by damper or valve means which is adjusted by geared motor means 22, Whereas the flow of cooling air through cooler I3 and conduit I9 is adjusted by damper means 2| adjusted by geared motor means 23. In addition to adjusting its respective valve or damper means, motor means 22 also adjusts a rebalancing potentiometer 24, and motor means 23 adjusts rebalancing potentiometer 25. These rebalancing potentiometers are adjusted by the shafts which drive the respective damper means and serve a purpose to be later described. Motor means 22 and 23 are conventional reversible geared motors adapted to adjust their respective dampers and follow up potentiometers in a relatively short time. These motors preferably include internal switches for limiting the travel of the driven shaft, although obviously any conventional limit switch means may be used. Also, for motors not harmed by stalling, limit stops may be used instead of switches. Although any reversible motors may be used, I prefer the common two-phase capacitor type motor for this use.

While it has been noted that heat is added to the air used for Ventilating the zones of the cabin by the compressing of the said air, and while this heat may sometimes be excessive in amount, it might also be inadequate to meet the demands in the respective zones. Therefore, means are provided for supplying added heat to the zones. As a source of heat, a conventional combustion type heater may be provided, or heat exchangers receiving heat from the exhaust of the engine may equally well be used. The source of heat is of little importance in the present invention, hence the specific means for providing the heat has not been shown. Assuming that a supply of heated air or gases is available, the same is delivered through main duct to the heat exchangers as follows: from main duct 30 through duct |05 to heat exchanger I 03, through duct 205 to heat exchanger 203, through duct 305 to heat exchanger 303, and through duct 405 to heat exchanger 433. These heat exchangers are conventional and have one set of passages for the heated gases and another set of passages for the air to be heated. Damper means |06, 206, 306 and 406, adjusted by geared motor means I 01, 201, 301 and 401, respectively, are provided for controlling the flow of heated gases through the respective ducts and heat exchangers. In addition, motor means |01 also adjusts a rebalancing potentiometer |08, it

being driven from the same shaft as damper means |06. Rebalancing potentiometers 208, 333 and 408 are driven by their respective motors 201, 301 and 401, respectively, in the same fashion.

Motor means |01, 201, 301 and 401 are each preferably two-phase reversible geared type m0- tors including limit switches, and are similar to motors 22 and 23 previously described excepting that the gear trains are such that their operating rotation is opposite to that of motor means 22 and 23. Obviously, identical motor means could be used by merely reversing the leads to motors 22 and 23.

With the apparatus as above described, it is now noted that air is supplied to the zones of the aircraft cabin through branch ducts I0 and II, main duct I4 and the respective branches to the individual zones. With damper |06, which controls the supply of heat to heat exchanger |03, shown in a closed position, it may be assumed that Zone |0| is suiciently warm that no heat needs to be added by heat exchanger |03, consequently the air passing to the zone through duct |02 possesses only its heat of compression. Damper 226 is shown in a partly opened position; hence, it may be assumed that zone 20| needs some heat in excess of that furnished by the heat of compression of the air entering through duct 202. Therefore, a limited amount of heated air or gas is permitted to pass through duct 205 and heat exchanger 203 to additionally warm the air passing through the said duct 202 into zone 20|. As shown, damper 306 is in a closed position; hence, zone 30| appears to need no added heat, as in zone |0| With the damper 406 in a wide open position, it would appear that maximum heat is demanded in Zone 40| and that the air entering through duct 402 is being additionally warmed by the maximum amount of heat that can be delivered through duct 405 and heat exchanger 433 to the air passing through duct 402. It is thus noted that dampers |06, 206, 306 and 406 control the addition of heat to the air delivered to the respective zones, and dampers 20 and 2|, which control the flow of air through the after-coolers, control the cooling of the air going to all of the Zones. As before noted, each of the present dampers is controlled by its own motor means; hence, it will be seen that the control of these motors is an important part of the present invention.

The means for controlling the present motordriven dampers comprises a compound electrical network comprising individual networks for each zone and an additional network for the aftercoolers. As each of the present networks ||0, 2|0, 3|0 and 4|0 in the respective zones is essentially similar, network ||0 will be fully described and numbered and the other networks will be less fully numbered and described although the description of the same will be considered to be the same as that of network ||0 excepting that numbers with a proper first digit for the zone involved are used.

Network I0 includes input terminals III and H2, output terminal ||3 and another output terminal comprising wiper ||4 of rebalancing potentiometer |08. The upper right-hand branch of network I|0 includes wire H5, xed resistor IIS, wire ||1, and. the portion of resistor ||8 of follow-up potentiometer |08 which lies above wiper H4; the lower right-hand branch of the network comprises the portion of resistor IIB lying below wiper H4, wire IIS, and iixed resistor |20. The lower left-hand branch of the network includes wire |2|, a temperature responsive resistor, or thermistor, |22, and a control point selector resistor |23 having an adjustable wiper |24. The upper left-hand branch of the network comprises fixed resistor 25 and wire |26. In addition, a differenti-a1 adjusting potentiometer having a resistor |28 and an adjustable wiper |29 is connected in parallel with resistor ||8 to permit an adjustment of the potential drop across resistor H8. Input terminals and 2 of the network are supplied current from secondary winding |30 of transformer 33 which has a primary winding 34 energized from a suitable source of alternating current. Secondary winding |30 is connected to terminals and ||2 by wires |3| and 32, respectively. Networks 2 0, 3 0, and 4 il are similarly energized from their respective secondary windings 235, 33%! and 43o of transformer 33. it will further be noted that wiper i4 of network il@ ,is connected by wire |40 to output terminal ZSB of network 2l; wiper 2|4 of network 2i@ is connected by wire 245 to output terminal Bit of network 3H); wiper 3|4 of network 3m is connected by wire 340 to output terminal `493 of network 4H), and wiper 4| 4 of network 4|!! is connected by wire 440 to output terminal 35 of network St.

As actually constructed, network 36 would likely be differently arranged and the transformer supplying current to the same would correspond to transformer 33, hence, the primary winding of the transformer of this network is numbered 34 to point out this similarity. Of course, a diierent transformer could be used, care being taken to keep the phase relation of the same correct.

Network 36 includes a tapped secondary winding 3l connected in series with fixed resistor 33, wire 39, resistor 4D of follow up potentiometer 24, resistor 4| of follow up potentiometer 25, xed resistor 42, output terminal 35, xed resistor 43 and secondary winding 3l. A center tap 44 of said secondary winding is connected by wire 45 to the junction between resistors and 4|. In addition, a potentiometer having a resistor 46 and an adjustable wiper 4'! is connected in parallel with resistor 40 between wires 39 and 4.5. Further, a similar potentiometer having a resistor 48 and an adjustable wiper 49 is connected in parallel with resistor 4| in a similar fashion. These potentiometers are used for adjusting the potential drop across resistors and 4|, respective, for adjusting the operating diierential of the after-cooler motors. The other output terminal of network 36 comprises either wiper 5B of rebalance potentiometer 24, or wiper 5| of rebalance potentiometer 25.

For a purpose which will become apparent, it is necessary that isolating transformers 242, 342, and 442 be used. Transformer 242 includes a primary winding 243 and a secondary winding 244, these windings being of a l-l ratio and having a relatively high impedance. Windings 343, and 344 of transformer 342, and windings 443 and 444 of transformer 442 are similar to those of` transformer 242. Transformer primary winding 243 is connected by wire 245 to terminal 2|3 and to wiper 2|4 by wire 245. Likewise, winding 343 is connected by wire 345 to terminal 3 3 and is connected to wiper 3 |4 by wire 346. Winding 443 is connected by wire 445 to terminal H3 and the said winding is connected to wiper 4|4 by wire 446. While it is noted that these isolating transformers are necessary in the control apparatus as shown, it is noted that they may be eliminated by providing an additional bank of contacts on the sequence switch, tobe described.-

As is customary in the case of network circuits for controlling a condition, as in the present case,- suitable amplifying means must be used to makethe output signal of the network circuits suffi-- ciently large to control the aforementioned motors. While a plurality of amplifiers might be used in a circuit of the present sort, I prefer to use a single amplier 52 of the electronic sort and to use it for each individual network, as well as the compound network, by alternately connecting it in the desired manner by sequence switch means. In the present apparatus, any

` conventional motor controlling amplifier capable of controlling one circuit when a suitable signal of predetermined phase is impressed upon the input terminals of the said amplier, and capable of controlling another circuit when a signal of opposite phase is impressed upon the same. As an example of an ampliiier-relay unit of this sort which has been found very satisfactory, reference is made to an application of Albert P. Upton, Serial No. 437,561, filed April 3, 1942, now Patent No. 2,423,534, issued July 8, 1947. Obviously, amplifiers of a different sort, such as a polarized relay, can also be used.

To permit the use of but a single amplierrelay unit in the present system, a sequence switch 54, driven by a geared motor 55 is provided. Three banks of switching contacts, 55, 51 and 53 and including movable switch blades 60, 6| and 62, respectively, are provided. Wipers 60, 6| and 62 are simultaneously actuated by a shaft s3 driven by motor 55. Each bank of contacts on the present switching means comprises six stationary contacts to be connected in a manner to be described. Generally speaking, switch bank 56 determines which network is connected to the amplifier, switch bank 51 connects one winding of the respective motor with the amplifier, while switch bank 58 connects the other winding of the respective motor to the amplifier.

With the present apparatus thus generally described, the relation of the various parts will bev made more clear by the following description of operation.

Operation In considering the operation of the present the airplane is considered as being divided into four zones. Air is furnished to all of the zones through conduits l0 and which lead from suitable compressors, as previously noted, and is delivered to the individual zones through conduit means previously described. The air furnished to the zones possesses heat of compression and may or may not need further heating, depending upon the conditions. Further, it may: need cooling and thus require use of after-coolers I2 and I3. To provide added heat, the previously` mentioned source of heat, such as a combustion heater or a heat exchanger associated with the exhaust system of one or more of the engines of the airplane, provides heated air or gases through conduit 30 to the respective heat exchangers associated with each air duct leading to a zone, as before described.

To put the present system in operation, it is necessary that the various units of the same be energized. Sequence switch 54 -is energized by the circuit: line wire 1||, wire 14, motor 55, wire l5r and line wire 1|. Amplifier-relay unit 52 is energized by the circuit; line wire 10, wire 12, amplifier 52, wire 13 and line wire 1|. Likewise, primary windings 34 and 34 are also energized from line wires 15 and 1| by circuits not shown. Suitable switches, not shown, may be used to control the energization of the above mentioned apparatus, but assuming that the line wires are energized and the apparatus connected as described, the system is now in readiness for operation. It is noted that the damper motors are energized through circuits controlled by the amplier, as will be noted in the following description.

It is noted that the present networks are energized by alternating current and amplifier-- relay unit 52 has been described as one which controls one circuit when a signal of a predetermined phase is impressed upon it and controls another circuit when a signal of an opposite phase is fed into it. However, it is rather confusing to describe the present series of networks in their operating relation in terms of phase of the signal voltages involved. It is more convenient to consider the present network during the instant of a half cycle during which time direct current relations hold. Thus, a condition in which a leading voltage would be present is analogous to a positive potential and a condition of a lagging voltage is analogous to a negative potential. Speciiically, in this description, the left-hand terminals of the transformer secondary windings may be considered positive and the right-hand terminals negative. It should therefore be kept in mind as this description proceeds i that phase relations rather than relative potentials are actually involved.

As previously noted, network ||0 is in control of zone |0|. This network receives current from secondary winding of transformer 33 through input terminals and ||2, and its output signal is taken from terminal ||3, grounded, and wiper IM, as noted in the previous description. Now, if wiper |29 is adjusted so that a two-volt potential will exist across resistor ||8 and a one degree change in temperature at thermistor |22 will alter the balance of the network by one volt then it may be assumed, when the network is also suitably adjusted by shifting wiper |24 over resistor |23, that the network is balanced when the temperature affecting thermistor |22 is '72"4 and wiper I4 is at the upper extreme of resistor itil, or with the temperature at thermistor |22 at '10 and wiper ||4 at the bottom extreme of resistor HB. With the network balanced as shown and the temperature at thermistor |22 at '12", a drop to 70, and with no rebalancing taking effect, will result in wiper ||4 becoming two volts positive relative to terminal ||3.

With the apparatus in the position shown, and with a drop of temperature at |22, resulting in wiper ||4 becoming positive relative to |!'3, as previously1 described, a signal is impressed on amplifier 52 by the circuit: wiper H4, wire |45, contact and blade 8|! of switch bank 56, wire 68, terminal 69 of amplifier 52, terminal 65`of the amplifier, wire and wire 61 to grounded terminal ||3 of network ||0. With a positive signal impressed on amplifier 52, the following circuit controlling operation of damper |16 is energized: terminal 18 of amplier 52, wire 19, switch blade 6| of sequence switch bank 51, contact |52, wire |53, terminal |54 of motor |01, terminal |5|, wire |50, Wire 259, wire 11 and common terminal 16 of amplifier 52. Also, current is supplied the motor ||1 from terminal 18 by the circuit: terminal-18, wire 91, condenser 98, wire 59, terminal 8B, wire Si, switch blade 62 of bank 53, contact |55, wire |55 and terminal |51 of motor |01. Due to condenser 95, the voltage applied to terminal |51 leads that applied to terminal |52; hence motor |01 is caused to operate in a direction to drive damper |55 toward an open position. As damper |06 moves toward an open position, heated gases ilowing from conduit 3|! through conduit |55 and heat exchanger |93 warm the air flowing through conduit |62 and thus tend to raise the temperature in zone il. In addition to increasing the temperature of the air flowing into zone liii, operation of damper |56 in an opening direction also results in driving wiper i Iii downwardly across resistor ||8. As wiper ||4 moves downwardly across resistor H8, it becomes less positive relative to terminal il?, and normally will eventually reach a point at which the network is balanced and the positive signal ceases. When this happens, and no signal is f ed into the amplifier, the aforementioned circuit to motor |01 is opened and the said motor stops operating. Had the temperature alfecting |22 been 71, movement of motor 51 would have continued until wiper H4 was driven approximately half way across resistor i i8 before the network could be balanced. However, had the temperature been '10 at thermister |22, a lull opening movement or" damper and a corresponding movement of wiper ||4 to the bottom oi resistor H3 would have been required to balance the network. A further drop in temperature would be of no avail in increasing heat because once the damper is driven to wide open position, limit switches prevent further operation of the motor and, as the damper is in wide open position, no more heat can be added. Because the equipment provided for furnishing heat in an aircraft is generally very powerful, it is contemplated that damper |66 will be driven to a fully open position only under most unusual conditions.

'With damper |66 open and wiper ||4 near the bottom of resistor H8, the air being delivered through duct |52 into zone possesses not only its heat of compression but is also further heated by the gases flowing through heat exchanger |03 under control oi damper |65, as previously noted. With large quantities of heat being provided for zones Ii, the inevitable result is a rise in temperature which is reflected in an increase in resistance of thermistor |22. Assuming that wiper lill is at the bottom extreme of resistor ||8 and the temperature at thermistor |22 becomes 71; wiper lil will now be one Volt negative relative to terminal i3, hence a negative signal is impressed on amplifier 52 by the same circuit previously described. A negative signal impressed on amplier 52 causes current to iiow through the following circuit: terminal of amplifier 52, wire 8|, switch blade 62 and terminal |55 of switch bank 58, wire |56, terminal |51 of motor |01, terminal 5|, wire |56, wire 259, wire 'Vl and common terminal 16 of the said amplier. Also, the other winding of motor E01 is energized by the circuit: terminal 85, wire 99, condenser S8, wire 91, terminal 1S, wire 19, switch blade 6| and contact |52 of bank 51, wire |53 and terminal |54 of motor |51. The voltage applied to terminal |54 now leads that applied to terminal |51; hence, motor |61 is caused to operate in a reverse direction and drives damper |55 in a closing direction. This direction of operation also causes movement of wiper ||4 upwardly across resistor I8 and thus makesV wiper I|4 less negative with respect to terminal H3. If the temperature at |22 remains at 71, the network would then become balanced when wiper ||4 reaches the mid point of resistor |I8. However, if the temperature continues to increase and rises to 72, movement of damper |06 will continue toward closed position and wiper ||4 will continue to be driven upwardly until it reaches the upper extreme at which point the network is again balanced: .there is no signal fed into amplifier 52, and the circuit causing closing movement of damper |06 is opened, thereby stopping motor |01. If the temperature in zone should continue to increase even though damper |06 has been driven to a closed position, the network becomes unbalanced with wiper |4 becoming more negative with respect to terminal I |3 as the temperature at I 22 increases. Further rebalancing of the network is impossible because wiper H4 is at the extreme of its movement and limit switches in the motor prevent further operation in a closing direction. If the temperature at |22 should rise to 73, wiper ||4 would then become one volt negative relative to terminal ||3 or, if the temperature rose to 74, wiper I I4 would then be two volts negative relative to terminal ||3. For reasons which will appear later, it is con- Venient to consider that the present heating cycle in zone l 0I has resulted in over-heating the zone to the extent that the temperature is 74 and there is an unbalanced signal from the network wherein wiper 9| 4 is two volts negative relative to terminal H3.

In discussing the operation of the present apparatus as it relates to zone |0I, it has been assumed that the network was continuously in charge of motor |01. However, since the signal connection to the amplifier and the controlling connections from the amplifier to the motor are through sequence switch 54, these connections are periodically interrupted. Assuming that sequence switch 54 is operated so that blades 60, 6| and 52 make one revolution per minute, then each contact is engaged by its respective switch blade for less than ten seconds. This works out very well for the amount of readjustment of the respective dampers needed each minute is quite small. Further, the slight delay between the periods at which control is exercised permits conditions within the zones to become somewhat more stabilized thereby rendering the system less erratic. Assuming that the sequence switch rotates in a counter-clockwise direction, it is noted that after the switch blades leave contacts |46, |52 and |55 they next engage contacts 246, 252 and 255. Further, after leaving these contacts the blades then engage the third set of contacts, then the fourth, i'lfth, sixth, and then repeat the cycle, as is obvious.

If it be considered that the sequence switch has operated so that the switch blades are on the second set of contacts, then network I I0 is no longer in charge of amplier 52 and network 2I0 is connected in controlling relation to the said amplifier. The connections are as follows: output terminal 2|3 and wiper 2|4 of network 2| Si are connected to primary winding 243 of transformer 242 by wires 245 and 246, respectively. Secondary winding 244 of said transformer 242 is connected through wires 241, 248 and 65 to terminal 65 of amplier 52 and through wire 245, contact 246, switch blade 60, and wire S8 to input terminal 69 of the said amplier. As before noted, windings 243 and 244 of transformer 242 have a 1-1 ratio 4and a relatively high imthe said transformer.

pedance. Thus, whatever signal is impressed on the primary winding of the transformer, the same signal is taken from the secondary winding of This assumes that the windings of these transformers are arranged so that the left terminal of each secondary winding will be at the same potential as the left terminal of the respective primary winding. The effect on the amplifier is just the same as if terminal 2|3 was directly connected to terminal 65 of the amplifier and wiper 2| 4 directly connected to terminal 69, as in the previous example. However, the present isolating transformers are used to prevent the conditions of balance of the other networks from affecting the signal from the network in question. As previously noted, by providing an additional bank of contacts on the sequence switch, the present isolating transfcrmers can be eliminated but lack of space has prevented this in the present figure. These isolating transformers are made with a relatively high impedance so that, when the networks are connected in series, as will be described, the shunting effect of each isolating transformer on its respective network is negligible. Assuming that the adjustments of network 2|0 are similar to those of network |I0, and the network is thus balanced when the temperature at thermistor 222 is 72 and wiper 2|4 is at the top of resistor 2|8; or, at a, temperature of 71, the wiper 2|4 is in the mid point of resistor 2I8; or, at a temperature of 70, wiper 2 I4 would be at the bottom of resistor 2I8, changes of temperature in zone 20| will have the same controlling eiect as those in zone IGI. With the network balanced as shown and with a temperature of 71 at 222, a decrease vin temperature at 222 will cause wiper 2|4 to become positive relative to terminal 2 I3 and thus cause a positive signal to be impressed on ampliiler 52 by the aforementioned circuit. This will cause a further opening movement of damper 206 by the circuit: terminal 16 of ampliiier 52, wire 19, switch blade 6|, terminal 252, wire 253, terminals 254 and 25| of motor 201, wire 250, wire 258, wire 259, wire 11, and terminal 16 of the amplifier. Also, terminal 18, wire 91, condenser 98, wire 99, terminal 80, wire 3|, switch blade 62 and contact 255, wire 256 and terminal 251 of motor 201. Likewise, a rise in temperature at 222 causing an increase in resistance at 222 will tend to make wiper 2|4 negative relative to terminal 2| 3 and thus cause a negative signal to be impressed on the amplifier. This will cause energization of a circuit as follows: terminal of amplier 52, `wire 8|, switch blade 62, terminal 255, wire 256, terminal 251, terminal 25|, wire 250, wire 258, wire 259, wire 11 and common terminal 15; in addition, terminal 80, wire 99, condenser 98, wire 91, terminal 18, wire 19, blade 6| and contact 252, wire 253 and terminal 254 of motor 201. Energization of this circuit causes motor 201 to operate in a damper closing direction. It is thus seen that the operation of network 2I0 is exactly the same as that of network IIl excepting that the signal is furnished to the amplifier through a 1-1 ratio transformer instead of directly as in the previous example. For reasons which will appear, it is convenient t0 assume that the temperature in zone 25| is 7l" and the network is in balance, as shown.

The relation of network 3|0 in zone 30| to its controlling motor 301 is precisely the same as the aforementioned network and the operation is the same as that described. AWith a drop in temperature in zone 30|, damper 306 is adjusted to an open position and wiper 3 I 4 is moved downwardly across resistor 318 while an increase in tempera- 'ture in the zone causes damper 306 to be driven to a closed position and wiper 314 is adjusted upwardly across the said resistor. Likewise, with the network balanced with wiper 314 at the upper end of resistor 318 and with a temperature of 72 at resistor 332, an increase in temperature at thermistor 322 to 73 will result in wiper 314 becoming one volt negative relative to terminal 313. For reasons which will appear, it is convenient to assume that the temperature in Zone 301 is 73 and there is a one volt negative signal from this network.

Likewise, network 410 in zone 401 performs the Vsame function relative to motor 40'1 as did the previous networks relative to their motors. In

this example, as in the others, a relatively low temperature in the zone causes motor 401 to drive damper 406 in an open direction and move wiper 1.14 downwardly across resistor 418 and an increase in temperature in the Zone causes an upward movement of wiper 414, as before described. With the parts in a position shown, it may be assumed that the temperature in the zone is 70,`

full heat is being called for, and the network is balanced.

It has now been shown that each of the four zones oi the aircraft cabin is provided with its own individual heat control apparatus effective through a common amplifier. A single amplier is sufficient for the several zones because a sequence switch sequentially places each of the networks in control of the amplifier and simultaneously places the amplier in control of the proper motor. It is further noted that zone 110 was assumed to be at a tempera-ture of 7 4, hence the network for that zone was unbalanced to the extent of a two volt negative signal. Network Z in zone 201 was balanced due to a tempera- :'.zf

ture ci 7 D 'and a midpoint adjustment of wiper 214; zone 301 was at a temperature of 73, hence network 318 was unbalanced to the extent of a negative signal of one volt and network 410 was balanced at a temperature ci 7G". It was previously pointed out that these networks are connected in series and it will now be observed-that Ythe cumulative unbalance of all of the networks is three volts negative. This follows because wiper 114 is 2 volts negative with respect to .i

grounded terminal |13; terminal 213 is at the same potential as wiper 1 14, and because network 250 is balanced, wiper ZES is also at the same potential, that is, negative 2 volts. Terminal 313 is at the same potential as 214 but wiper 314 is one volt negative with respect to terminal 313. Therefore wiper 314 is 3 volts negative with respect to terminal 113. Terminal 413 is at the same potential as 3 I 4 and wiper 414 is at the same potential as terminal 413 due to the balanced .if

condition of network 410, hence wiper 414 is 3 volts negative with respect to grounded terminal 113.

When sequence switch 54 operates so that its blades are on the fifth set of contacts, all of the previously mentioned networks areconneoted in series with network 36 to control amplifier 52 by the circuit: wiper 51, wire 83, contact 546, blade 60, wire 68, terminal 69 of amplifier 52, terminal 65, wire S5, wire 61, terminal 113, network 110, wiper 114 of said network, wire 140, terminal 213, network 210, wiper 214 of said network, wire 240, terminal 313, network 310, wiper 314 of said network, lwire 340, terminal 413, network 410, wiper 414 of 'said network', wire 440,

" ing damper pera-ture.

l2 terminal 35, and network 36. Network 36 is so connected that it is in phase with the other networks previously considered. Therefore, if it be assumed that the bottom end of secondary winding 3l is at zero potential, the upper end of the same would have a positive potential. It follows that, due to resistor 42, terminal is negative relative to the bottom end of resistor 41. For the purpose of this description, it will be assumed that the bottom end. of resistor 41 is at a potential one volt higher than terminal 35. Resistor 42 is used to stabilize the system by requiring at least a predetermined unbalance of the compound network before the aftercooler motors can be operated. The value of this resistor is more or less arbitrarily chosen. It may further be assumed that wipers 4'! and 49 oi adjusting potentiometers 43 and 48, respectively are so adjusted that 'there is a three volt drop across resistor 40 and also a three volt drop across resistor 41. With conditions as thus established, if terminal 35 is at zero potential (neglecting the unbalance voltages across networks 110 to 410) the bottom end of resistor 41, and wiper 51 in the position shown, are at a potential of positive one volt. In this case, motors 22 and 23 are so connected to amplier 52 that the circuit closed by a negative potential being impressed on the amplifier causes operation of the motors to open their respective dempers. This direction of motion, different from that of the previously described motors, is due to the aforementioned reverse gearing in these motors. Therefore, with a potential at wiper 51 of one volt positive, the damper 21 is closed and further operation of motor 23 is prevented by the limit means of the said motor. Likewise, wiper is at a potential of positive four volts and damper 20 is closed with further motion of motor 22 prevented by the limit means of the motor.

Ii it now be assumed that terminal 35 is at a potential of negative three volts, due to the aforementioned summation of unbalances of the network in the zone, then wiper 51 would be at a potential of two volts negative. This signal impressed on amplifier 52 by the previously described circuitwould cause motor 23 to be energized in a damper opening direction by the circuit: terminal 83 of amplifier 52, wire 81, switch bla-de 32, contact 555, wire 89, terminal 0l of motor 23, terminal 3E of said motor, and wire 38 to ground. Normally, instead oi merely going to ground, wire 83 would connect with common and grounded terminal i6 of amplifier 52, but this connection has not been shown for lack of space.

In addition, the other winding of motor 23 would 'be energized by the circuit: terminal 30, wire 99, condenser S3, wire S2, terminal 70, wire 79, blade 81, Contact 552, wire 84, and terminal 85 of motor Energizing this circuit of motor 23 causes it to drive damper 21 in an opening direction thereby permitting aftercooler 13 to cool the air passing through duct 11 so that the air furnished to the Zones will be somewhat lowered in tem- The air furnished through duct 14 and the respective Zone ducts will then tend to increase the heat load in the zones requiring heat, but will tend to lower the temperature in the zones that are over heated. In addition to driv- 2! in an opening direction, wiper 25 is adjusted upwardly across resistor 41. If it be assumed that terminal 35 was at a potential o three volts negative, then wiper 25 would. be

across resistor 41 before the signal would be v ,13 rebalanced and the negative signal to amplier 52 wiped out. At the same time that the signal to amplifier 52 is being diminished by the rebalancing effect of wiper 25, the cooler air furnished the zone is having an eiect of its own. The cooler air furnished to zone IIB will tend to reduce its temperature and therefore reduce the unbalance of the network thereby reducing the negative signal i'rom the said network. In zone 29|, the cooler air being furnished to the same will merely result in damper 296 being driven slightly more open to add more heat to the air to maintain the temperature at the desired level. In Zone Sil i, the reduction in air temperature will tend to restore the balance of the network and thus diminish the negative signal from network Sie. A reduction in air temperature furnished to sono dei would still further increase the heating load, but as maximum heat is already being furnished to this zone and no further rebalancing can take place, any further drop in temperature below 20 will result in a positive signal from network die. This positive signal will tend to oppose the negative signals remaining from networks il@ and 32d. If it be assumed that the net signal now left from all of the zone networks is one volt negative, then wiper i is at a potential three volts positive to terminal 35 or two volts positive with respect to the bottom end of resistor di. This positive signal impressed on amplifier '52 causes energization of a circuit as follows: terminal 'i9 of amplifier 52, wire 19, switch blade Ei, Contact 552 of switch bank 51, wire 85, terminal S5 of motor 23, terminal 86 and wire BS to ground; also terminal 18, wire 91, condenser 98, wire 99, terminal 8|), wire 8|, blade 62, contact 555, wire 89, and terminal 8l of said motor. This causes a reverse action of motor 23 which drives damper 2| toward closed position and drives wiper 5i toward the bottom of resistor 4|.

lf the signal at 35, resulting from considerable overheating in the zones, was at a potential of four volts negative relative to ground, wiper 5| would need to be driven to the upper end of resistor 4| to rebalance the compound network and wipe out the negative signal being impressed on amplifier 52. This would result in a Wide open position for damper 2i. If the overheating in the zone should be even more pronounced and result in a signal at terminal 35 of, for instance, six volts negative, it will be noted that this negative signal cannot be rebalanced by movement of the wiper 5|. While wiper 5|, in moving to the upper end of resistor di could rebalance a negative signal of four volts, there would still remain a negative signal of two volts. Therefore, when the sequence switch adjusts its blades to the sixth set of contacts a two volt negative signal is impressed on amplier 52 by the circuit: wiper 60 a more conventional condition 5i), wire 9B, contact ddii, blade 69, wire 5S, terminal 59 of the amplifier, terminal 65, wire 66, wire El, grounded terminal H3, network IIIJ, wiper ||4, wire 45, terminal 2I3, network 2li), wiper 2|4, wire 24e, terminal 3%3, network SI5, wiper 3| 4, wire 35d, terminal cl3, network M0, wire 449, and terminal 35 ci network 39. This negative signal causes an opening movement of damper 2l) by the circuit: terminal 89 of amplier 52, wire 8|, switch blade B2, contact 955, wire 96, terminal 95 of motor 22, terminal 93, wire 94 to ground; also, terminal 89, wire 99, condenser 98, wire 97, terminal "i8, wire 19, blade 6|, Contact |552, wire 9| and terminal 92 of the motor. The energization 'of thislcircuit causes motor 22 to drive its-damper in an opening direction and to adjust wiper 59 upwardly across resistor 4U. As in the previous example, to rebalance a negative signal of two volts on wiper 59, it would be necessary to adjust the said wiper 2/3 of the way upwardly across resistor 49 before the network would again be balanced and the negative signal to the amplifier wiped out. Therefore, the air furnished to the Zones through duct I4 would` be cooled to the maximum by after-cooler I3 and cooled to approximately 2/3 capacity by after-cooler I2. As noted previously, the cooling of the air supplied to the zones reduces the over-heating of the same and lowers the negative signal that comes from the respective networks and may even cause a positive signal from some Zone that requires more heat. This would tend to diminish the negative signal at terminal 35 of network 36 and thereby cause wiper 59 to become positive relative to terminal 35 and cause a positive signal to be impressed on amplifier 52 by the aforementioned circuit. A positive signal impressed on amplifier 52 will cause a closing movement of damper 20 by the circuit: terminal 'I8 of amplifier 52, wire 79, switch blade 6 I., contact 65'2, wire 9|, terminal S2 of motor 22, terminal 93 of said motor, and wire 94 to ground; also, terminal 18, wire 91, condenser 98, wiper 99, terminal 89, wire 8|, blade 62, contact 555, wire 89, and terminal 95 of the motor. Energie-ing of this circuit causes a reverse movement o1"- motor 22 which drives damper 20 to closed position and adjusts wiper 5D downwardly across resistor 49.

While the Apresent description relates the action of various control means in steps, it is obvious that many of the functions of the present apparatus are simultaneously performed. For instance, the balance of a network is ailected substantially simultaneously by adjustment of the respective wiper and also by the eiect of changing the damper position associated with the said wiper. In addition, it should be kept in mind that the individual network, or the compound network, is only in control of its respective damper motor for a few seconds and thus can only make a partial adjustment in response to demand. If further adjustment is needed in the same direction when the sequence switch again reaches its previous position, further adjustments will then be made in the same direction. If conditions have changed during the cycle of the sequence switch, then the respective damper motor will be operated in response to the new condition.

While the present apparatus has been rather specifically set forth, it is obvious that many modications and substitutions are possible. Further, the present teachings are useful in condition control systems generally. To give a concrete example of the use of the present system in control system, reference is made to the following description of Figure 2.

Figure 2 In Figure 2, the present system is shown as ap plied to a more conventional heating apparatus such as may be used in an aircraft, a railway car or a residence. Four zones are used as before, and because the zones and the control networks are the same as in the prior illustration, the same numbering is used in this illustration.

In this ligure, the hot water boiler 69| applies heated water through pipe 602 and .branches |62, 262, 352 and 452 to heat exchangers |6I, 26|, 436| and'- 46|, respectively, located in zones IUI, 20|

| and 4M, 'as shown. The return flow from the heat exchangers is taken through branches 63, 263, 363 and l63, pipe 603, circulator 6M, and pipe 625 back to the boiler. The circulation of the heated water to the heat exchangers in the ree spective zones is individually controlled by valves located in the supply branches such as valve ISG in branch 62. Valve [55 is adjusted by geared motor means I6?, this motor means being prefe erably of the same sort previously described. Likewise, valve 266 is adjusted by motor means 261, valve 355 by motor means 351 and valve 466 by motor means 461.

Fuel is supplied to boiler i through conduit 605, the fuel flow being controlled by a conventional solenoid valve 669 and a proportionally adjustable valve 565, driven by geared motor means 567. Motor means 557 is similar to the other motor means described and isgeared to operate in the same direction as the other motor means. For a purpose which will appear, by-pass means T controlled by solenoid valve 6&8 is arranged around valve 565 to permit operation cf the lboiler even if valve 556 is closed. Additional control means for boiler 60! comprises a high limit control GID adjusted to open its contacts when the boiler water reaches a predetermined high temn perature, such as about 215 degrees. Further, a low limit control Eil is provided which is adjusted to close-its contact when the boiler water temperature drops below a predetermined value, such as 90,

In addition to motor means 67 adjusting valve means ISG and'operating potentiometer wiper I I4, as in the previous example, said motor means also operates a mercury switch means 69 by means of a cam |68. The cam is so adjusted that the contacts of the switch are open when valve |66 is closed and wiper il@ is at the top of resistor I I8. However, the adjustment is such that the initial opening movement of valve IE6 results in tipping switch 69 so that its contacts will be closed. In a similar fashion, motor means 26'! operates switch means 269 by means of cam 268, motor means 36? operates switch means 368 by means of cam means 368, and motor means 561 operates switch means 069 by means of cam 468. As will be noted, each of these switch means is capable of controlling the operation of circulator means 604.

Amplifier-relay unit 52 is the same as that described in the previous illustration and has been similarly numbered. Sequence switch 654 is generally similar to that of Figure 1, but includes 4 banks of switches each having 5 contacts. In this switch means, motor means 655 drives shaft 664 which carries switch blades 660, SGI, 662 and 563. Motor means 655 may comprise any suitable geared motor capable of driving the switch means at the required speed, such as one revolution per minute.

To control the present system, the same electrical networks IIS, 2I0, 3I0 and M0, previously described, are shown in zones IBI to 40| respectively. Although the present networks are the same as previously described, the isolating transformers are omitted in this case, due to the provision of another bank of contacts on the sequence switch. Because these networks are the same as previously described, the same numbering has been retained. As in the previous illustration, the individual networks in the zones are connected in series with a further network identified as 536. Network 536 comprises a secondary Windingr 53] forming part of transformer 33 and connected 628 and wire 613.

in series with fixed resistor 50|, output terminal 502, fixed resistor 593, a nonresistance slide portion 58d, resistor 5535, wire 506 and resistor 5l. The other output terminal of the network comprises wiper 508 which is adjusted across slide portion 504 and resistor 5535 by motor means 561. Terminal 502 is connected to wiper M4 by wire 440, and the cumulative condition of balance of the networks in the respective zones is rebalanced by adjustment cf wiper 508 across resistor 505. Resistor 553 is used to make slide portion 504 about two volts negative relative to terminal 502 so that an imbalance of the zones of at least two volts is required before a positive potential can appear on wiper 560. The function ci this network, as well as that of the rest of the apparatus will be described in greater detail in the following operation schedule.

Operation of' Figure 2 For convenience in the present description, it will be considered that each of the networks in the zone is adjusted to be in balance with a, temperature ci 72 affecting the thermistor of the said network and with the follow up potentiometer wiper, i It for instance, at the uppermost extreme of its respective resistor. The system is energized similarly to that of Figure 1 with motor 555 of sequence switch 654 being energized from the line wires by the circuit: line wire l5, wire 14, motor i355, wire i5 and line wire 'I I. Amplifier-relay unit 52 is energized by the circuit: line wire il), wire l2, amplifier 52,'wire 'I3 and line wire 1I. Primary winding 3Q, of transformer 33 is connected to the line wires by suitable wiring, not shown. Likewise, wires 6I2 and BIS of the boiler control apparatus are connected to the line wires in a suitable fashion. Also, wires 6M and SI5, for energizing circulator 604, are connected to a suitable source of current by wiring, not shown. With the apparatus energized and the parts in the position shown, it is noted that wiper IM in zone lill is at the upper extreme of resistor IIS, hence valve H56 is closed and the contacts of switch IGS are open. In zone 20|, wiper 2 lll is at the mid-point of resistor 2 I8, hence it is assumed that valve 255 is approximately half open, and the contacts of switch 260 are closed. Assuming that network 2 I6 is balanced in the position shown, it would then appear that the temperature in zone 29E affecting thermistor 222 is 71. In zone 35i, wiper 3M is at the upper limit of resistor SIS, valve 366 appears to be closed and the contacts of switch 365 are opened. As in zone lill, it may be assumed that the temperature affecting thermistor 322 is 72. In zone l, wiper M4 is seen to be at the bottom of resistor 4I8 thus indicating that valve 466 is wide open, and the contacts cf switch 450 are seen to be closed.

With both switches 25S and 469 closed, circulator 65?@ is operating by the circuit: wire 6I5, wire GIG, switch 6:39, wire 6I?, wire ISIS, circulator 604, and wire SIG. Circulator 604 is also energized by a parallel circuit as follows: wire 6I5, wire 6I9, wire 620, wire SEI, switch 259, wire 622, wire G23, wire 624, wire SIS, circulator 604, and wire 6M.

With wiper 5258 at the extreme left of slide portion 564, it follows that val-ve 556 is closed, but yassuming that the system has just been put into operation, and that the water in boiler 60I is less than for instance, the boiler is furnished fuel through valves 658 and 60,9. Valve 609 is opened by the circuit: wire 6I2, high limit control 6I0, wire 628, wire 627, solenoid valve 509, wire This permits gas to flow through either valve ses or ley-pass so'l. However, as before noted, valve 566 is closed. Valve 608 is opened by the circuit: wire 6|2, high` limit control 6H), wire 26, wire 629, low limit control 6H, wire Stil, solenoid valve E538, wire 63! and wire 6|3. As the boiler water temperature is below the predetermined value of 90, the contacts f low limit control 6i i' are closed thereby permitting valve til-'E to be opened and permitting gas to flow through cy-epass del to operate the boiler. The oy-pass iid? may be considered to have a suicient capacity to operatethe boiler at a relatively low level, such as 20 per cent of its maximum capacity. With the boiler being heated by iiowing through by-pass E91, it willr be noted that as the boiler water temperature rises above 90, limit control will open its contacts and thus close solenoid valve tilt. it will'be seen that the purpose of the low limit control Sli and solenoid. valve 523 is to maintain the boiler water at a sufficient temperature to provide small increments of heat to the zones immediately upon there being a demand for the same. The high limit control uit is used to control main solenoid valve E509 to prevent further iiring of the boiler when such operation would become dangerous. The present control means for the boiler are con sidered to be illustrative only and form no part oi' the present invention.

With boiler SGI operating, and water of approximately 90 F., temperature being circulated through supply pipe 662 and returned' through pipe tds, circulator 6&4 and pipe 625 back to the boiler, it is noted that this heated water is supplied to zone 20| due to valve 256 being about half open and is also being supplied to zone 49|- dueto valve @Sii being entirely opened. None oi this water is being supplied to zone lili or 3`|- because valves H56 and 365i are closed. Due to the relatively low temperature of the water supplied the heat exchangers 25| and 45|'in zones 26| and dill, respectively, only a light heat' load can be taken care of without further operation of Y the boiler. However, if the structure including the several zones is subjected to conditions considerably increasing the heat load, the temperature in each of the zones may fall. With a decrease in temperature at thermistor 22, wiper i4 tendsto become positive relative to terminal H3, hence, a positive signal is impressed on amplifier ii2`b'y the circuit: wiperV H4, wire |1|, wire i12, contact 13, blade ttl, wireES, terminalV 69 oi amplifier 52, terminal 65 of said amplifier, wire te, and wire 61 to grounded terminal i i3 of network ili. As before noted, this imposes a positive signal on the amplifier which causes motor means i6? to be energized in a valve opening direction by the circuit: terminal 18, wire 19, switch blade 652, contact |14, wire |15, terminal i513 of motor means |51, terminal |5I, wire |59, wire v| 1E and common terminal 16. Also, the other winding ci motor means 51 is energized by the circuit: terminal 18, wire 91, condenser 98, wire SS, terminal 89, wire 8|, switch blade 663, con* tact |11. wire |18, and terminal |51I of motor means |61. This energizes motor means |51 in a manner to drive valvel toward open position and to move wiper H4 downwardly across resistor im. So long as the temperature affecting thermistor |22 does not drop below 70, wiper Il!! will be moved until the network is balanced,` as in the previous example. Assuming that a considerable heat load has been imposed on the zones, as before noted, and the temperature -con- 1 tinues to drop in spite of the fact that wiper |4 is moved tothe bottom or resistor H8, thus indicating that valve |66 is wide open, each de-V gree drop in temperature below 7U", and with wiper lili at the bottom of resistor' i i 8,'will result in kwiper H4 becoming one volt more positive relative to terminal |13. For reasons which will appear, itmay be assumed that the temperature affecting thermistor |22 reaches 68, thus making the'unbalance of network l'li two volts positive; As an incident to opening of valve ist, it should benoted that switch i 68 was tipped to close its contacts, so that if there had been no demand for operation of theV circulator by any oi the other zones,l switch |59 could have placed the same in operation.

If sequence switch |354 now operates its blades to the next set of contacts, network 2li? of zone iti' will be'placed inv charge of amplifier 52 by the circuit; wiper 244, wire 21|, wire 212, contact 223', blade GSI', wire terminal 69, terminal 65; wire EE, wire 633, blade 66D, contact lis-d, wire 635i, wire iii, wiper IM', wire Mil, and-terminal' 2|@ of network 2li). Also, it is noted that ter-r minal of the amplifier is grounded by the circuit: ternn'nal 55, wire Se, wire 61 to grounded terminal l l 3' of network lili. With a heavy heat" load being imposed on zone 25|, the temperature in the same will be' considered to fall and as itY fallsbelow 7l", wiper/2M becomes positive relative to terminal 2li thus causing' operation of motor mea-insA 253'! by the circuit: terminal 18, wire is," switch blade 552, contact 21e, wire 225i, terminal 2540i motor means 261, terminal 225i, wire 232, wire i151, wire B15 and terminal 15. also, the other winding of the motor means is energized bythe circuit: terminal 18,y wire el,`

condenser d2, wire`9'9, terminal, wire 3i, blade @#33, Contact 211, wire 218, and terminal 251 of motor means 261. As before noted, this will operation of motor means .251 in a directionito further open'valve v286 and to drive wiper 2id' downwardly across resistor 223. This will continueso long as ther motor is permitted to operate andl until. wiper 2M' reaches the bottom oli-resistorl 2id. Ii' thetemperatureV should continueto drop, the network wouldbecome unbalanced and,.if`the temperature should reach 692, for. instance, wiper 2|6 would become l volt positive relative to terminal 2| 3.

In a similar manner, when Vthe switch blades ofthe sequence switchadvanceto the next set oi contacts, network 3|() .of zone 30| would be placed in Charge of amplifier 52 by the circuit: wiper 3M; wire 31K, wire 312, contact 313, blade iii, wire 613, terminal E59; terminal 55, wire wire E33, blade 65u, contact 655, wire 5st, wire 21|, wiper 2M, wire 24!) 'and terminal 352 oi network Siti, Terminal E5 of ampliiier iig remains grounded by a circuit previously traced. With network iilin charge of amplier the ampli-y fier will then 'cause suitable operation of motor 351 to adjust valve Siiii'in a 'manner to meet the heat requirements of the zone and to adjust wiper 3M in adirection to'rebalance the network in a liti and; 2lb. TheI energizing circuit for the motor'can be traced' in exactly the same manner as the-energizing-circuit formotors ifi? and 25? with the'excep-tion Lthat the contacts, wires and terminals lstart withva higher number corresponding tov-the zone in question. present, it Twill be assumed that the temperature in zone 39:! v'does not drop below-'70", hence netwerk ti'iil'will'beassumed to be in balance and therewill'- beino signal resulting from the same.

fmanner similar to that described for networks For the At the next step in the operation of sequence switch 654, and withthe blades on the fourth set of contacts, network 4|0 of zone 40I' is placed in charge of amplifier 52 by the circuit: wiper M4, wire 41 I, contact 413, blade 66|, wire 68, terminal 69, terminal 65, wire 66, wire 633, blade 660, contact 668, wire 669, wire 31|, wiper 3I4, wire 346 and terminal 4|3 of network 4|0. With network 4|0 in charge of amplier 52, changes in temperature affecting thermistor 422 will affect the balance of the network and thereby the signal imposed on amplier 52 in the same manner as would the previous networks. Likewise, motor 461 will be operated in one direction or another in the same manner as the previous motors. In the position shown, wiper 4|4 is at the bottom of resistor 4I8, indicating that valve 466 is wide open. This would also indicate that the temperature at thermistor 422 which resulted in this arrangement was relatively low. Assuming that the temperature drops due to the heavy heat load previously noted, it may now be considered that the temperature of the zone is at 67; hence, wiper 4|4 may be assumed to be 3 positive relative to terminal 4|3. While a positive signal at the wiper of a network generally operates to cause opening of the valve, it is obvious that the valve cannot be driven beyond wide open due to the limit or stop means associated with the motor.

At the next position of the blades of the sequence switch, a compound network including networks IIO, 2|0, 3I0, 4|0 and 536 is placed in control of amplifier 52 by the circuit: wiper 508, wire 616', contact 513, blade 66|, wire 68, terminal 69, amplifier 52, terminal 65, Wire 66, wire 61, terminal H3 of network IIO, network ||0, Wiper ||4, wire |40, terminal 2|3, network 2I0, wiper 2M, wire 240, terminal 3I3, network 3I0, wiper 3I4, wire 340, terminal 4|3, network 4|0, Wiper 4I4, wire 446, terminal 502 and network 536. Assuming that resistor 503 is of such resistance value that the slide portion 504 is two volts negative relative to terminal 502, then it will appear that wiper 508, in the position shown, with a twovolt positive signal from Vzone IDI, a one-volt positive signal from zone and a three-volt positive signal from zone will be at a potential 4 volts positiverelatiye to grounded terminal H3. With amplifier V52 energized as above described, it causes operation of motor means 561 by the following circuit; terminal 18, wire 19, blade 662, contact 514, wire 515, terminal 554 of motor means 561, terminal 55|, wire 556, wire I8I, wire |80, wire |19, wire |16 and terminal 16 of amplier 52. The other winding is energized by the circuit: terminal 16, wire 91, condenser 98, wire 59, terminal 80, wire 8|, blade 663, contact 511, wire 518 and terminal 551 of the said motor means. This causes operation of motor 561 in a direction to open valve 566 and to move wiper 508 to the right across slide portion 504 and resistor 505. However, due to slide portion 564, the beginning movements of Wiper 568 to the right causes no rebalancing due to the lack of resistance of the slide portion. This is provided so that any opening movement of valve 566 will be sufficient to cause proper operation of the burner. For the purpose of this discussion, it may be assumed that valve 566 should be at least 2O per cent open for such proper operation. Therefore, slide portion 504 would be of such a length that the wiper would traverse it while valve 566 is driven to a 20 per cent open position. If there is a rive-volt potential difference existing across resistor 505, then it appears that wiper 508 must be driven most of the way across resistor 505 before the 6 volt positive signal at terminal 502 can be rebalanced. This will mean that valve 566 is nearly wide open and boiler is operated at a high level of capacity. It will be noted that it is possible for valve 556 to open and supply fuel to the boiler at the saine time that valve 608 and bypass 601 is open, but it will be obvious that the relatively large fuel supply to the boiler will quickly raise the boiler water temperature above the low limit setting of controller 6|| and thus open its contacts. When the contacts of 6|I open, valve 668 is closed and full control of the "fuel supply to the boiler is assumed by valve With the boiler water temperature raised to a relatively high value due to the large supply of .fuel being furnished the boiler, the temperature "in each of the zones may be rather rapidly increased. In zone IOI, for instance, it was assumed that the temperature had reached 68, valve |66 was wide open and wiper |44 was 2 5 AAvolts positive relative to terminal |I3 of the network H0. With a full supply of relatively hot water being supplied heat exchanger |6I, the temperature may be assumed to rise above 70 in the zone and thus make wiper |I4 negative ,relative to terminal I|3. If the sequence switch 'his assumed to be in the position shown, so that network IIB is in charge of the amplifier again, a negative signal is then imposed on the amplier by the circuit previously traced. The negative .signal causes operation of the amplier in a manner to control motor |61 by the circuit: terminal 80, wire 8|, blade 663, contact |11, wire |18, terminal |51 of motor means |61, terminal I5|, wire |50, wire |16 and terminal 16 of the Iamplifier. The other winding of the motor is energized by the circuit: terminal 80, wire 99, condenser 98, wire 91, terminal 18, wire 19, blade 662, contact |14, wire |15 and terminal |54 of the motor means. It will be noted that this circuit for controlling motor means |61 is the same as that previously traced with the exception that condenser 96 is in the circuit supplying current to terminal |54 instead of the circuit supplying current to terminal |51. The effect of this is to ,cause operation of the motor |61 in a reverse direction from that previously described. A reverse operation of motor |61 causes a closing movement of valve |66 and advances wiper ||4 upwardly across resistor IIB to rebalance the lnetwork. As the temperature rises above 70, the network will then be kept in balance by sufficient movement of I I4 in the manner noted.

With the blades of the sequence switch 654 advancing to the second set of contacts, thus placing network 2 i 0 in charge of amplifier 52, a similar operation of this network may be considered in exactly the same manner as that of network I I0. As the temperature rises in zone 20| due to the large supply of heat available, the temperature affecting thermistor 222 will increase its resistance as the said temperature rises and makes wiper 2I4 less -positive relative to terminal 2|3. When the temperature rises above '10 in the zone, the network can be rebalanced in a manner previously described and the positive signal will be removed. As the sequence switch continues to operate, and networks 3|0 and 4I0 are successively placed in control of the amplier, any positive signal resulting from low temperatures in the zones will be reduced as the zone 21.. temperatures rise in the manner just discussed. When the sequence switch reaches the th set of contacts and the compounded network is again in charge of the amplifier', it will be noted that the summation of positive potentials, previously six volts, has now been reduced. Assuming that the sum is .three volts, then wiper 508 in its previously noted right-hand position will be three volts negative relative to terminal H3 and a reverse Operation of motor '557 will be called for in the same manner that reverse operation was required of motor i6?. vThe reverse operation of motor 557 will cause a closing movement of valve 555 and a movement of wiper 508 to the left across resistor 5de. The closing movement of valve 5st will reduce the supply of heat to the boiler and thus decrease the temperature of the water being supplied to the zone. Also, the reduction in boiler water temperature will decrease the heat supplied to the various -Zones so that the rate of temperature rise in the same will be slowed. Thus, it will be seen that boiler 6l!! is operated just sufciently to meet the heat demands of all the zones while the heat supplied to the individual Zones is regulated in accordance with the temperatures in the Said zones.

While this invention has been rather specifi? cally described in the present disclosure, it is clear that many substitutions and equivalents are obvious. For instance, any conventional moe tor can be used instead of the two-phase capacitor type motors described. Further, a two-phase motor such as described may be operated by an amplifier of the sort described, which, instead of operating relays, energizes one winding of the motor. The other winding of the motor is en-` ergized directly from the line, with a condenser in the circuit. It is noted that this type of ampliiier-motor control is also disclosed in the aforementioned. Upton application. As these and many other substitutions and equivalents are feasible, it is considered Athat the scope of the present invention should be determined only by the appended claims.

Y.I claim as my invention:

1. In a control system, a plurality of devices to" be controlled, a reversible motor means `for each of said devices, amnliner means, sequence switch means for sequentially placing `said ame plifie'r in control of Aeach of said motor means, a plurality of network circuits each including an impedance variable in response to a predetermined condition, an additional network circuit, means connecting all of said network circuits in series, and means including said switch ie'argis for sequentially and individually connecting 'each of sai-:l condition responsive network circuits in control oi said amplifier Ymeans substantially simultaneously with the connection of a motor means with said amplifier means, said 'switch means also sequentially connecting the series of all of said network circuits in control rof vsaid amplier means substantially simultaneously with the controlling of another of said motor means by said amplifier means.

2. In control apparatus for a lplurality of zones, means for changing a predetermined condition in each of said zones, means in each zone responsive to said condition for independently controlling said condition changing means, individual `:followup means operable in response to operation or each of said condition `changing means, the operating range of said follow-up means being less than that oisaid condition vref sponsivemeans, additional means operable to change said condition in all of said zones, means: connecting said zone condition responsive means and said additional means in series, and followup means 'operable as a function of the operation of said additional condition changing means for supplementing said rst Inamed follow-up means by rebalancing the cumulative imbalance of the series of networks.

3. In a temperature changing system for a plurality of zones, a central means for chang- ,ing the temperature of a medium, means for distributing the medium to heat exchange means for each of the Zones, means for regulating thev ldistribution of said medium to each of said zones,

an electrical network means including an impedance variable in response to temperature change in each sone for controlling said regulating means, means for varying the capacity of said central means, and means connecting said network means in a manner to control said varying means in response to the total demand forv change of temperature of said medium.

der pressure to each of said zones, means for cooling lfsaiel air, means for individually heating the air supplied to each of the Zones, means responsive to the temperature of each zone for controlling the heating means for that zone, and means responsive to vall of said temperature responsive means for controlling said cooling mea-ns.

6. 1In an aircraft having a cabin divided into a plurality of zones, means for supplying compressed having -heat of compression to each of said zones, mean-s for individually additionally heating the air supplied to each of sai zones, afterf-.cooler means for removing heat oi pression `from said 4compressed air, an electrical network circuit including a thermistor for each zone, switch means for sequentially placing each network circ-uit into controlling relation 'with its respective individual heating means, and circuit means including said switch means and all of said network circuits for controlling said means.

7. In` .a structure supplied with compressed air, sa-id structure being divided into a plurality of Zones, means for individually varying the temperature of the air vsupplied to each of zones, means responsive to the temperature in each ofsaid :zones for controlling said varying means, means for varying the temperature of the supply of compressed air, and means .for connecting each of 4said condition responsive means together for jointly 4controlling the means -ior varying the temperature of the compressed air Supply A8. Ina-control system, a plurality of devices to be controlled, a reversible motor means for operating each of said devices, amplifier means `for controlling'said motor means, sequence switch means having a plurality of banks of contacts, one bank of contacts sequentially controlling after-cooler lconnectionsfbetween the amplifier vand a winding of each of the motor meanaanotherbank ol4 then said series of network circuits, in controlling relation to said amplifier means.

9. In a temperature changing system for a plurality of zones, a central means for changing the temperature of a medium, means for distributing the medium to each of said zones, means for regulating the distribution oi said medium to said zones, an electrical network for each zone, said network each including an impedance variable in response to temperature change within the respective zones, means for connecting each of said networks in controlling relation to its respective distribution regulating means, means for varying the temperature changing capacity of said central means, and means for connecting said network in series to control said varying means.

10. In a condition control apparatus for a plurality of condition changing devices, a series of independently operable electrical network circuits each arranged to control one of said devices and capable of becoming unbalanced in response to a need for change in said condition, and additional network including rebalancing means arranged to control another condition changing device, and means connecting said additional net-v work into said series of networks so that said` rebalancing means can rebalance the sum of the unbalance of all of said network circuits.

l1. In control apparatus for a plural zone'central heating system, central means for heating medium, means for distributing the heated medium to the zones, individual means for controlling the supply of heated medium to said zones,

individual means responsive to the temperature of said zones, each of said temperature responsive means being arranged to control its respective individual supply controlling means, and means connecting said temperature responsive means together in a manner to control said cen-k tral heating means, each of said temperature re sponsive means operating through part of its range to control its individual supply controlling means and through another part of its range to control said central heating means.

12. In control apparatus of the sort described for a plurality of zones, means for changing a condition in each of said zones, an electrical network for each of said zones including an irnpedance variable in response to changes in said condition for controlling said condition changing Y means, variations in said impedance altering the balance of said network, means operable in response to operation of said condition changing means for restoring the balance of saidnetwork y within prescribed limits, additional condition changing means, means connecting all of said networks together for controlling said additional condition changing means, and means operable in response to operation of said additional conditionrchanging'means for restoring the balance of all of said networks as a whole. Y

13. In control apparatus, a plurality of electricalnetwork circuits,-means for altering the balone of said network circuits inlIl() 24' ance of at least two of said network circuits, means for partially rebalancing each of said network circuits, means responsive to the cumulative unbalance of the partially rebalanced networks.

; and means for rebalancing the said cumulative unbalance of said networks.

14. In control apparatus, a plurality of series4 connected normally balanced electrical networks,

means 'for altering the balance of said networks. means for partially rebalancing said networks individually, and means including an additional network connected to said series for rebalancing the cumulative unbalance of the series of networks.

15. In a structure having an enclosure divided into a plurality of zones, means for supplying air under pressure to each of said zones, first means for changing the temperature of said air, means for individually changing the temperature `vof the air supplied to each of the zones in a sense opposite that of said first means, means responsive to the temperature of each zone for controlling the individual temperature changing means for that zone, and circuit means in- `cluding all of said temperature responsive means for controlling said first temperature changing means.

i6. In a control system for a plural zone temperature changing apparatus, means for supply- `ing temperature changing medium to each of said zones, rst means for changing the temperature of said medium for all of said zones, second means for changing the temperature of said medium for each individual zone, means individu- ;ally responsive to the temperature of each of said zones for controlling the respective second temperature changing means for its zone, and means responsive to the sum of the responses of said temperature responsive means for controlling I-said rst temperature changing means.

17. In apparatus for a temperature changing system for a plurality of zones, first means for changing the temperature of said zones, an elec-` trical network circuit including a resistor variable in response to the temperature changes for each of said zones, second means for changing the temperature in each of said zones, means in- Y cluding the network circuit associated with one of said zones for controlling the second temperature changing means for that zone, and means including a plurality of said network circuits in series for controlling said iirst temperature` changing means.

18. In control apparatus for a plurality of sec- Y ondary control devices and a primary control device, a plurality of network circuits each including a rebalancing potentiometer and a resistor variable in response to a desired condition,

an additional network including a rebalancing potentiometer, means for connecting all of said networks in series, and means for placing each network in control of said primary device.

19. In control apparatus of the sort described; a plurality of normally balanced electrical net-l works connected in series, each of said networks including means responsive to a predetermined condition and being capable of being unbalanced by such response, means for individually rebalancing a given amount of unbalance of each network, means responsive to the algebraic sum of 75- the existing imbalances of each of said networks,

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,170,072 Hartig Aug. 22, 1939 2,188,775 Locke Jan. 30, 1940 2,238,433 Nessell Apr. 15, 1941 2,351,695 Newton June 20, 1946 2,408,699 Sparrow Oct. 1, 1946 

